Method and apparatus for feed-forward control of wood pulp refiners

ABSTRACT

Method and apparatus for producing wood pulp stock having substantially constant drainage characteristics from raw stock, that is drainage rate variable, by making a laboratory determination of the functional relationship between drainage rate and refiner applied specific energy for the desired stock furnish. Using the functional relationship to coordinate signals from a continuous or rapidly cycling drainage rate measurement meter on the raw stock line as an automatic, feed-forward setpoint control to a stock refiner control system, where the control system is capable of altering the magnitude of specific energy applied to the stock so as to accommodate the set-point as a variable reference standard.

United States Patent 1191 Blume June 11, 1974 William M. Blume, Charleston Heights, SC.

[73] Assignee: Westvaco Corporation, New York,

22 Filed: July 25, 1972 21 Appl. No.: 274,999

[75] Inventor:

[52] US. Cl 162/198, 162/253, 162/254, 162/261, 162/263, 241/33 [51] Int. Cl. D2lb l/l4, D2lf 7/00 [58] Field of Search 162/254, 253, 263, 261, 1 162/198; 241/30, 28, 33, 37

[56] References Cited UNITED STATES PATENTS 2,346,746 4/1944 Green .f. 162/263 X 2,734,378 2/1956 Meyers 162/263 X 3,144,763 9/1964 Mayo 73/63 3,186,215 6/1965 Danforth.... 162/198 X 3,538,749 10/1970 Danforth 73/63 4/1972 Keyes et al. 162/254 9/1972 Rummel et a1. 162/254 X Primary ExaminerSv Leon Bashore Assistant Examiner-Steve Alvo Attorney, Agent, or Firm-Richard L. Schmalz; W. Allen Marcontell [5 7] ABSTRACT Method and apparatus for producing wood pulp stock having substantially constant drainage characteristics from raw stock, that is drainage rate variable, by making a laboratory determination of the functional relationship between drainage rate and refiner applied specific energy for the desired stock furnish. Using the functional relationship to coordinate signals from a continuous or rapidly cycling drainage rate measurement meter on the raw stock line as an automatic, feed-forward set-point control to a stock refiner control system, where the control system is capable of altering the magnitude of specific energy applied to the stock so as to accommodate the set-point as a variable reference standard.

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PATENTEDJM 1 1 014 3816241 SHEET 30? 4 hwmlu xookm Em PATENTEDJun 1 m4 SHEET k 0F 4 STOP 2 AIR SUPPLY METHOD AND APPARATUS FOR FEED-FORWARD CONTROL OF WOOD PULP REFINERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to automated control of wood pulp refining engines.

2. Description of the Prior Art Refining engines, as characterized by the papermaking art are wood pulp preparation machines that induce fibrillation along the surface of the cellulose fiber. When bonded together, the intertwined fibrils increase the structural tenacity between adjacent fibers to improve the tensile and bursting characteristics of the finished paper. However, tear resistance of the finished paper is diminished by such fibrillation. Consequently, to achieve an optimum balance between these contradictary effects of refining, the degree of fibrillation must be carefully controlled.

For any given paper, each of these characteristics, tensile, bursting and tear strength, may be related, by a determinable function, to the magnitude of refiner work imparted to the pulp stock (specific energy) from which the paper is formed.

Specific energy consumption is a work per unit of stock mass relationship and is usually determined in kilowatt-hours per ton of stock or some equivalent thereof such as BTU per ton of stock. Specific energy may be the calculated product of such measurable parameters as stock flow rate, stock consistency and refiner motor current supply or stock flow stream temperature differential across the refiner engine.

Also related by a determinable function to the refiner work on the pulp stock are the water holding properties of the stock. These properties describe the ease with which water passes through papermaking fibers while they are being forced into a wet mat on the fourdrinier screen of a paper machine. A free pulp drains readily whereas a slow pulp drains its waterslowly. Consequently, for the given pulp stock, a measure of such water retention properties may provide adirect indication of tensile, bursting and tear characteristics of a paper to be produced from the pulp stock.

Numerous tests have been devised to quantify pulp stock properties of water retention. Typical among such tests are the Canadian Standard Freeness Test wherein a 1 liter sample of standard consistency stock is allowed to flow freely into a funnel. Flow from the funnel is restricted by an orifice of select size. A side outlet is selectively positioned in the funnel wall. That portion of the 1 liter sample not accommodated by the flow rate of the orifice is drawn ofi for volumetric measurement as a quantity of the pulp freeness. A low volume represents a free" stock whereas a'high volume represents a slow" stock.

Another type of water retention property test is that for drainage factor. This quantity may be determined by forming sheets on a British standard sheet machine under standard conditions and taking the drainage time and weight of the test sheets. The drainage factor is the slope of the line produced when drainage time is plotted against weight of stock added to the sheet machine.

Units for drainage factor are in seconds per gram.

A third test for pulp water retention, the Bolton- Emerson test, is a variation of the drainage factor test wherein the weight of the test sheet is standardized for a test series. In the Bolton-Emerson test, standardized volume of pulp slurry having a standardized consistency is passed through a screen of such mesh as to v allow the passage of water but not fiber. The test sample is subjected to standardized pressure differential conditions across the screen. These conditions leave only the time factor as a variable in the test, the weight of pulp, quantity of water and pressure drive being standardized. Accordingly, to obtain a quantitative measure of freeness or slowness, one need only measure, in seconds, the time interval required to separate the fiber from the water. A low time interval indicates a free stock whereas a high time interval is indicative of a slow stock.

Lacking in all the above described water retention property tests is consideration for the vibratory dynamics actually present on the fourdrinier wire. Since the drainage performance of a pulp on the fourdrinier wire is generally characterized, in the art, as drainage rate," any test for pulp water retention properties independent on the fourdrinier shall be characterized for purposes of this disclosure, as a test for static drainage rate.

If, in a particular mill, producing a particular pulp, the raw stock, direct from the digesters or defiberizing engines, had consistent water retention properties, it would be a relatively simple matter to merely control, in adirect manner, the magnitude of refining energy applied to the stock in order to consistently achieve the desired retention property at the paper machine headbox.

However, many uncontrollable factors'influence the raw stock retentionproperty such as the moisture content and species characteristics of the raw wood furnish to the digester. Accordingly, the degree of digestion and defiberization necessary to yield a constant raw stock retention property is continuously changing for practicably indeterminate reasons.

Consequently, it is of limited value to the papermaker to know exactly how much refining energy he will or has applied to the raw stock since he doesnt know exactly how much energy is necessary for the run of stock, then flowing, to yield the desired retention property as an end result.

If the papermaker knew, precisely, the retention properties of the presently flowing raw stock, at the time the power setting of the refiners must be determined, he could do so with confidence. However, the known and accepted tests for such properties are, definitively, of a batch or incremental nature, usually performed under the exact conditions of a laboratory. Such test procedures are much too slow and cumbersome to provide the papermaker with refiner control information at the time it is needed.

In lieu of a timely water retention property test of the stock, papermakers have relied on the indicated vacuum drawn from the flat box or couch roll of the paper machine fourdrinier section as a continuous measure of these properties. US. Pat. No. 2,699,095, Re. No. 24,185 and No. 3,654,075 are examples of automatic refiner control systems that are monitored by vacuum measurements taken at the fourdrinier section.

Although fourdrinier section vacuum is related to the final water retention properties of the stock, it is also related, unfortunately, to numerous other mechanical characteristics of the paper machine and web that are independent of water retention or drainage rate as it is called in connection with the fourdrinier. Disturbances or changes in the couch roll vacuum, therefore, may or may not be related to a change in the stock drainage rate. For example, an undetected mechanical change in the headbox slice lip opening of unobvious magnitude could cause a shift in the couch roll vacuum. If the vacuum shift is assumed to be drainage rate related, correction of the vacuum indication may be obtained by an appropriate alteration of the refiner energy application. This action, however, will establish a new balance between the adjusted drainage rate and the quantity of stock deposited by the new slice opening on the fourdrinier screen. Hence, the finished paper will be over or under refined for the desired mechanical characteristics and, moreover, will have an undesired basis weight.

Accordingly, couchroll or flat box vacuum offers an unreliable alternative to direct water retention property monitoring for refiner control.

Even if it were possible to reliably isolate fourdrinier section vacuum measurements due to stock drainage rate from those due to other sources, as is attempted by the teaching of US. Pat. No. 3,654,075, for example,

there would yet remain the wasted effort problem attendent with a feed-back control system. Whether practiced manually or automatically, any control system which monitors one or more quality characteristics of a product subsequent to the operational station responsible for the characteristics inherently tolerates the production of a small amount of error for the benefit of the larger amount. Of course, small and large are relative quantities and in years past, when a typical paper machine would produce approximately 2 tons of paper per hour, there would only be approximately 1 ton of refined pulp fiber in storage between the refiner and the fourdrinier wire. In other words, from the time the inferior quality condition was detected to the time it could be corrected, only 1 ton of inferior quality product need be produced.

By contemporary standards, a typical paper machine is supplied with 30 tons of pulp fiber per hour from as many as parallel flow refiners to produce as much paper product per hour. At this production rate, 5 tons of refined pulp fiber may be in storage between the refiners and the fourdrinier wire. If this storage stock is of inferior quality, the production of 6 tons of inferior and possibly unmarketable paper product must be produced before correction of the condition may be effected by the prior art feed-back control systems.

Although some effort has been given of late to continuous, on-line, measurement of pulp stock water retention properties as represented by US. Pat. No. 3,655,980 and the Aug. 21, 1961, publication in the Paper Trade Journal of an article entitled Continuous Freeness Measurement and Control, such teachings have not been widely adopted by the industry. Furthermore, no teaching is found to suggest that the specific energy input of stock refiners may be directly controlled by such prior art stock water retention measurement systems. More particularly, no teaching is found to suggest that pulp refiners may be directly controlled most advantageously by sampling the stock water retention property before refining for feed-forward control of the refiner energy input.

It is, therefore, an object of the present invention to teach the construction of a simple, on-line, rapidly cycling static drainage rate measuring device having reliability of performance characteristics comparable to laboratory determinations.

Another object of the present invention is to teach an automatic refiner control strategy pursuant to direct, static drainage rate measurement.

A further object of the present invention is to teach a feed-forward automatic refiner control stragegy.

SUMMARY OF THE INVENTION These and other objects of the invention may be achieved by electrically pacing and measuring the pneumatic control cycle of a Bolton-Emerson type of water retention property test meter disposed for continuously sampling raw pulp supply stock to refiners. Simultaneous with a water retention test, tests are also taken of stock temperature, consistency and pH. If test conditions are withinpredetermined limits, a signal proportional to measured water retention may be accepted as a reliable measure of static drainage rate. Said static drainage rate signal is processed, either manually or by computerized logic, to determine, from a laboratory and operationally developed history of the stock type, the magnitude of refiner work needed of the approaching stock to achieve a desired final static drainage rate. Signals proportional to the needed refiner work are then entered as set-point control signals to an automatic refiner control system such as is disclosed in US. Pat. No. 3,568,939.

DESCRIPTION OF THE DRAWINGS FIG. I is a flow diagram of the papermaking process between the digester vessel and the fourdrinier section of the paper machine.

FIG. 2 is a graphic plot of refiner applied specific energy as a function of static drainage rate for two pulp stocks distinct in furnish, as to wood species, and degree of cooking, as to Kappa number.

FIG. 3 is a composite plot against elapsed time of a typical change in the static drainage rate of raw stock to illustrate the consequent effect on couch roll vacuum and applied refining energy pursuant to a feedback corrective control system.

FIG. 4 is a composite plot against elapsed time of a typical change in the static drainage rate of raw stock to illustrate the consequent effect on couch roll vacuum and applied refining energy pursuant to the feedforward refiner control system of the present invention.

FIG. 5 is a stock flow piping schematic of the overall refiner control system of the present invention having superimposed thereon an integrated control logic flow schematic representative of the invention.

FIG. 6 is an integrated electrical-pneumatic circuitry diagram for the static drainagerate sampling device of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS chine chest 4; and, the interconnecting stock flow piping 2 and 3, also seen in FIG. 1.

To the raw stock chest 1, raw pulp stock is delivered from one or more pulp washers for blending. Subse- Signal 41 is an original emission from computer 2 R quently, the greater bulk of blended raw stock is 5 Proportional) the momentary p ifi ene gy applicapumped through conduit 2 for distribution to one or more refiners as represented by R,, R R A sample portion of blended raw stock is taken from the chest 1 through conduit in parallel flow with the trunk line 2 as a continuously flowing source reservoir for the static drainage rate meter 20. Instruments 21 and 22 in the test sample shunt 2a are a pH meter and a thermometer, respectively. Instruments 23 and, F provide electrical signals proportional to stock consistency and flow rate, respectively.

Before entering the refiners R R and R respectively driven by motors M M and M the stock flow rate respective to each refiner is measured by flow meters F F and F The stock flow stream temperature to each refiner is taken by thermometers 11, 12, and 13.

Refined stock emerges from the refiners into pipeline 3 to be measured of heat content again by thermometers 11a, 12a, 13a and thence carried to the machine chest 4 for further blending and storage before delivery to the paper machine head box.

Refined stock flow shunt 3a provides a sampling reservoir for a second static drainage rate meter and attendant instrumentation including flow meter F pH meter 31, thermometer 32 and consistency gauge 33. Although data from the static drainage rate meter 30 is not necessary to the feed-forward feature of this invention, such accessory data may be used advantageously for calibration and control trim purposes in a manner to be described subsequently.

Alternatively, data from the static drainage rate meter 30 may be used exclusively or primarily for a most efficient feed-back control system, if desired.

Elements A T,, A T and A T represent logic circuitry for receiving and comparing signals from respective pairs of thermometer ll-lla, l2-l2a, and 13-13a. Responsive to the comparison, computers A T,, A T and A T, transmit original signals proportional to respective stock temperature differentials.

Computer 2 R receives the temperature differential signals from computers A T,, A T and A T for mathematical combination and processing with signals proportional to the respective stock flow rates from meters F F and F All of these signals are combined by computer 2 R pursuant to the relation:

The calculated product of this relation is proportional to the specific energy (E applied by the several refiners to the stock, units being corrected to BTU per ton of stock. If units are desired in terms of kilowatt-hours per ton of stock, the temperature differential signals from computers A T,, A T and A T may be corrected by the appropriate mathematical equality for heat and power. Alternatively, current and voltage signals may be transmitted from the motors M M and M in lieu' of the stock temperature measurements for direct calculation of specific energy in units of kilowatt-hours per stock ton. This calculation would take the form:

tion of all refiners R R and R collectively.

Receiving signal 41 is refiner correction computer- 2 c for comparison to a set-point or reference signal 40. Computer 2 is the source of signal 40 and generates it in response to data received from the static system and processed as a function of laboratory and other applied data. In essence, signal 40 represents the magnitude of collective refiner applied specific energy that is needed to work the stock to the desired final water retention property. Accordingly, computer 2 0 compares the magnitude of specific energy that the refiners are momentarily delivering, as represented by signal 41, to the magnitude of energy necessary for the desired drainage rate, as represented by signal 40, and derives and emits a signal 44 proportional to the necessary change, if any, to the refiner engine effort needed to match the objective.

Although the aforedescribed system is perfectly adaptable to the control of a single refiner, such systems are more commonly utilized to control a multiplicity of refiners, in which case, it becomes necessary to allocate the energy correction signal 44 among the several refiners since some may be larger or more efficient than others and can take a disproportionate share of the needed change. Such allocation is the function of computer A which keeps an accounting of the present loading and capacity of each refiner. Operatively then, allocation computer A assigns that portion of the total needed correction, represented by signal 44, to each refiner R R R according to its individual need or capacity.

Signals 44a, 44b, and 440, then, are individually assigned portions of signal 44 and dictate'the refiner disc or plug setting via respective refiner controller C C and C Heretofore has been described a prior art refiner control system such as that more completely described in US. Pat. No. 3,568,939 except for the briefly described contribution of the static drainage rate responsiveness of set-point signal 40. It should be understood, however, that most of numerous other single and multiple refiner control systems are responsive to an externally provided reference signal to which the refiner control system can relate for control orientation. Consequently, the present invention may be adapted to any of such refiner control systems.

Regressing now, to focus on the static drainage rate measurement system in stock flow shunt 2a, it is seen from FIG. 6 that test meter 20 is merely a blind spur from shunt 2a having a sample barrel 29 separated from the shunt conduit 2a by a screen 28 of appropriate mesh as to permit the passage of water but prohibit the passage of pulp fibers.

Entering at the top of barrel 29 is a pneumatic conduit 14 having controlled communication with an air supply line 15.

lntemally of barrel 29 are lower and upper liquid level switches 24 and 25, the respective contact levels being separated by a precisely determined distance D to specify the desired test volume.

Pacing the entire operation of the static drainage rate test is a timing device K, set to transmit a single starting impulse to the initiating winding 1, for the purpose of closing starting switch S,. Timer K emits such a starting impulse at regular, periodic intervals determined by the desired cycle rate of the draining test, each 90 seconds, for example. The starting impulse is of selected magnitude and duration as is sufficient to close the contacts of switch S, long enough to establish sufficient electromagnetic force in winding H, to hold the switch S, closed. Thereafter, the starting impulse stops.

When winding I, is energized by the starting impulse from K, switch S, closes to energize holding winding H, and open solenoid valve 26. Communication of pneumatic conduit 14 is thereby established with the air supply subject to pressure controls 16. Pressure controller 16 holds the pressure in conduit 14 and, consequently, in barrel 29 at a constant, predetermined level that is slightly less than the pressure prevailing in shunt 2a so as to allow a fixed, pressure differential drive of the stock into barrel 29.

As the stock rises into barrel 29, the water vehicle thereof passes through screen 28 but not the fiber constituent. A fiber mat is established on the shunt side of screen 28 which inhibits continued transfer of water to a rate proportional to the water retention properties of the fibers. When sufficient water has passed the screen 28 to reach the lower reference level 24, the fibrous mat on screen 28 has grown with sufficient accumulation to provide a reliable water retention test. This event closes the contacts of lower level switch 24 to energize starting pulse circuit P,.

Starting circuit P, is of a prior art type that, in response to an energized input, emits a single signal pulse of select magnitude and duration. Thereafter, the pulse energy stops and will not flow again until the input energy stops and starts again. Therefore, so long as switch 24 is closed, starting circuit P, will not emit a second pulse.

The single pulse from starting circuit P, starts the running of a prior art elapsed time measuring device E. As the water continues to rise in barrel 29, the timer E accumulates data proportional to the elapsed interim.

When the water level has risen the prescribed distance D in the barrel 29, upper level switch 25 closes to energize a second'single pulse transmitting circuit P and stop the running of elapsed timer E. Also energized by the P pulse are time delays L,, L and switch S, reset relay 0,.

When reset relay 0, is energized, the holding circuit of switch S, is immediately opened to allow the mechanical bias of the moving contact point of S, to open the solenoid valve 26 holding circuit thereby closing the valve 26 and disrupting fluid communication between line 14 and the pressure controller 16. There being no energized bias on the switch 8,, the contacts thereof remain in the open position awaiting the next pulse from timer K.

In response to the stop pulse from circuit P time delays L, and L, merely retardthe signal for respective, predetermined time periods before passing it on.

The signal from time delay L, initiates a reset circuit W in timer E to transmit the accumulated time signal stored therein and clear the storage circuit for the next starting pulse from circuit P,. The transmitted signal is proportional to the measured static drainage rate of the tested stock and enters computer 2 as such.

Also energized by the delayed L, signal is initiating winding I for the switch S When closed, switch S conducts energy to a holding relay H to keep the switch S closed and to the actuating winding of solenoid valve 27. When open, valve 27 places pneumatic conduit 14 into controlled fluid communication with the air supply source again but at a pressure greater than the pressure of shunt line 2a. This pressure differential drives the test charge of water standing in barrel 29 down through the screen 28 and back into the flow stream of shunt 2a, cleaning the accumulated fiberous mat against screen 28 in the process.

Adequate time for the foregoing barrel purge is allowed by time relay L 'before transmission of the stop pulse from circuit P, on to the reset relay 0; to open the holding circuit H, of solenoid valve 27 holding switch S,. Valve 27 closes to interrupt communication between line 14 and the air supply, thereby stopping the purge of barrel 29.

Due to the falling liquid level in barrel 29, switches 24 and 25 have opened thereby resetting the start and stop pulse circuits P, and P in preparation of the next level switch closure due to rising fluid.

At this point, all circuits are quiet and open except for the continuing advancement of pace timer K. When the prescribed period has elapsed, the timer K issues another starting pulse to initiating winding 1, to start the cycle over again for another static drainage rate signal to computer 2 If correct static drainage rate was consistently equivalent to the raw measure signal, it would be sufficient to by-pass computer 2 20 for direct receipt of the timer E signal by computer 2 However, due to stock varia tions of pulp consistency, temperature and pH, a static drainage rate measure thereof may not be exactly equal to a true measure. For this reason, signals proportional to these parameters are also transmitted by instruments 23, 22, and 21, respectively, to computer 2 These auxiliary signals from 21, 22 and 23 may be handled in either of two ways. Each may be received by a respective limit circuit whereby if one or more of the auxiliary signals exceeds a predetermined value range, such as to render the signal from meter 20 unreliable, transmission of the static drainage rate signal to computer Z is interrupted.

Alternatively, computer 2 may be programmed with laboratory determined process data whereby a static drainage rate signal corrected to standardized conditions may be derived by computer 2 from the auxiliary signals notwithstanding the excursion of any one or more auxiliary signals from the standard value range.

Computer 2 constitutes the interface between the automatic refiner control system and the automatic static drainage rate determination system. Pursuant to this function, Z is programmed with data such as that represented by the graphs of FIG. 2. Static drainage rate signals from computer 2 20 are compatible with the scale of one graph axis, the Williams Slowness Scale along the abscissa in this example, and needed refining energy signals 40 to computer 2 c are compatible with the other axis of the plot.

2 must also be programmed with data concerning the desired end result. Such is the set-point input of FIG. 5 and may take the form of either a target specific energy value or a target static drainage rate value. Unlike the program data that is definitive of the specific energy consumption to static drainage rate function for the wood furnish and cook type, the set point is an operator entered variable needed by the computer to establish a presently desired end point on the characteristic curve. A typical event to dictate the operators change of the set-point input would be the desire for a grade change in the finished paper.

A representative operation of computer 2 may be thusly: Relative to FIG. 2, wood of furnish V is to be cooked to a K numberof Y. Accordingly, data that is definitive of the typical specific energy relation to static drainage rate for that furnish and cook is made available to the active control circuit.

The grade characteristics of the finished paper that is desired suggests the final static drainage rate which, in this example, constitutes a set-point value proportional to a Williams Slowness of 60 seconds. A corresponding total specific energy input of 160 kw-hr./ton will need to be applied to the stock. Accordingly, the operator enters a set-point value of 60 seconds into the manual entry station of computer 2 control console. Responsively, the computer reviews the programmed data stored within the active control circuit and determines that 160 kw-hr./ton is the refining energy target.

Due to the fact that the stock may have been previously worked," to some degree, by defiberizing engines at an earlier flow station, for example, signal 42 from the drainage rate computer 2 20 informs computer 2 that the stock in transit has a raw static drainage rate of IO seconds. From the internally stored data relative to the active stock curve, computer 2 20 determines that the static drainage rate signal 42 corresponds to an applied specific energy value of 70 kw-hr./ton.

From the foregoing determinations, computer )1 further determines that the magnitude of additional refining energy needed by the stock in transit to reach the desired total is 90 kw-hr./ton (160 kw-hr./ton desired minus 70 kw-hr./ton received).

A signal proportional to the needed addition of 90 kw-hr/ton constitutes the substance of signal 40 from computer 2 m and becomes the set-point signal for the automatic refiner control computer 2 To continue the example, assume that specific energy averaging computer 2 R is emitting a signal 41 to the effeet that the average specific energy currently being applied to the stock flow is 85 kw-hr./ton. Upon receipt of signal 40 representing a need of 90 kw-hr./ton, computer Z 6 compares this need value to the presently applied average value of 85 kw-hr./ton and determines that an additional kw-hr./ton should be applied by the refiners. Such is the substantive value of signal 44.

Allocation computer A receives the 5 kw-hr./ton increase dictate of signal 44 and determines how the 5 kw-hr./ton increase shall be apportioned among the several refiners.

If desired, the static drainage rate testing system in shunt 3a may be used as a feed back alternative to the feed forward system in shunt 2a described above. In this case, however, an initial assumption must be made relative to the static drainage rate of raw stock received at the refiner. Nevertheless, such a system may be more efficient than other, prior art, feed back systems, since the post refiner static drainage rate is sampled directly, no opportunity being given for the introduction of irrelevant parameters. Moreover, the post refiner stock sample is taken from the refiner discharge manifold 3 or machine chest 4 before the accumulation of large quantities of nonconforming stock.

As to the applied logic of computer 2 w in the feed back example, it may generally be characterized as the reverse of the feed forward system with an initial condition raw stock static drainage rate assumed and entered by the operator at the console manual entry station. The desired finished stock static drainage rate is also entered as in the case of the feed forward system. Actual or measured finished stock static drainage values are fed back to computer 2 w for comparison to the assumed, initial condition, values with the assumed raw stock rate being corrected as the consequence of an increase or decrease in the refining energy demand signal as is found necessary for the conformity of the actual or measured post refiner static drainage rate to the desired or set-point value.

As a third and preferred alternative, static drainage rate signals 42 and 43 from both test systems are offered to computer 2 10 simultaneously. Such data provides a reservoir of actual line information to correct the laboratory derived data forming the substance of the static drainage rate to refining energy function curves of FIG. 2. As operational time accumulates, the internally stored program data is corrected and honed to accuracy by the actual line measurements thereby increasing the corrective action response time of the refiner to a transient excursion of the raw stock static drainage value.

The significance of rapid response time and of the invention, generally, may be appreciated by a comparison of FIGS. 3 and 4. Therein, the couch vacuum is given as the reference value of performance rather than finished stock static drainage rate since the former parameter is more familiar to those of ordinary skill in the art. In both cases of FIGS. 3 and 4, couch vacuum disturbances are attributed exclusively to water retention property changes in the stock. I

The control relation between the measured couch vacuum and refining engine response of FIG. 3 is a simple feed back system comprising an alert and skilled papermachine tender taking note of an initial departure of the couch vacuum from an established norm. Responsively, the machine tender informs a skilled refiner operator of the changes which, in the personal judgment of the machine tender, are needed.

In contrast, FIG. 4 represents a system under group refiner control referenced by a feed forward static drainage rate set-point as described herein but without feed back correction of the internal program parameters. The reduced degree of couch vacuum departure from norm, asshown from a comparison of FIGS. 3 and 4, is typical of system performance from the present invention. Not only is the degree of couch vacuum disturbance reduced by the present invention but, as a comparison of the FIGS. 3 and 4 time scales will substanti ate, the invention eliminates the disturbance result more quickly.

The foregoing numerical examples are merely representative of several methematical manipulations that may be performed with the various accumulated data, measured, derived and assumed, to achieve the desired end result of assuring that the refiners, collectively, will apply sufficient work to the particular stock in transit so the average water retention properties of the ma chine chest 4 blend will remain at the desired level. To summarize, however, it will be appreciated that basic to the invention are at least one measured value of the stock static drainage rate; at least one assumed value of the desired stock static drainage rate; and, at least one derived value representative of a differential in average specific energy applied to the stock. Further, laboratory or experience derived data is necessary to relate the static drainage rate values to specific energy values or vice versa. From such data, the differential energy exerted by the refiners may be related in a quantitative manner, to the total or absolute energy adsorption level for the stock that is desired. From this relation, a quantitative value representative of change from a present refiner energy exertion level to a future energy exertion level may be derived. This change value offers a quantitative reference for refiner adjustment.

The mechanics of such mathematical manipualtions, whether performed manually or by electronic data process equipment, are well known to those of skill in the art. Accordingly, it is of no significance that the setpoint value for the target or objective refining level is: entered as a slowness value or a total specific energy of refining value; combined first with the value represented by either of signals 41, 42, or 43; or, entered by the console of computer 2 c or Z It will also be apparent to those skilled in the art that other changes may be made in the preferred embodiments described herein without departing from the spirit of my invention as set forth in the appended claims. Therefore, having now disclosed my invention, what I claim as new andunobvious and desire to secure by Letters Patent is:

l. A method of controlling the magnitude of energy applied to an aqueous slurry of pulp stock by at least one refining engine, said method comprising the steps of:

A. determining a quantitative first differential value of the average refining energy applied to said stock by refiner engine means; 7

B. determining a desired total quantitative value of average refining energy to be applied to said stock;

C. determining a quantitative value of total refining energy actually absorbed by said stock prior to working by said refiner engine means;

D. mathematically combining said determined values to derive a second differential value representative of a change in the magnitude of average refining energy application required of said refiner engine means for the average total value of refining energy actually absorbed by said stock as discharged by said refiner engine means to substantially equal said desired value; and,

E. adjusting the application of refining energy to said stock by said refiner engine means pursuant to the magnitude of said second differential value.

2. A method as described by claim 1 wherein the value of total refining energy actually absorbed by said stock is derived from a known functional relationship that a static drainage rate value bears to total absorbed refining energy for a stock sample that is representative of the subject stock.

3. A method as described in claim 2 wherein said value of total refining energy actually absorbed is derived from a measured value of static drainage rate for said subject stock.

4. A method of controlling the magnitude of energy applied to a flow stream of aqueous slurry pulp stock by pulp refining engine means, said method comprising the steps of:

A. obtaining a functional relationship between static drainage rate and total absorbed refining energy that is relevant to said stock;

B. measuring the static drainage rate of said stock at a point in said flow stream before said engine means;

C. deriving a first quantitative value from said measured drainage rate and said functional relationship that is representative of the total average specific energy that has been absorbed by said stock;

D. selecting a second quantitative value that is representative of a desired total average specific energy to be absorbed by said stock;

E. deriving a third quantitative value from the mathematical combination of said first and second values that is representative of a change in the magnitude of average specific energy delivered to said stock by said engine means necessary for said first value to substantially equal said second value; and

F. controlling said engine means in response to said third value.

5. A method of controlling pulp refining engine means as described by claim 4 additionally comprising the steps of:

A. producing signals proportional to said first and second values;

B. combining said first and second value signals to produce a third value signal; and

C. controlling said refining engine means responsively. to said third value signal.

6. A method of controlling pulp refining engine means as described by claim 5 wherein said first value signal is proportional to the measured time interim of a stock slowness test.

7. A method of controlling at least one pulp refining engine means comprising the steps of:

A. obtaining from measured parameters a first quantitative value representative of the average specific energy applied to a pulp stock flow stream by said engine means;

B. obtaining from measured parameters a second quantitative value representative of the average static drainage rate of said flow stream stock prior to working by said engine means;

C. selecting a third quantitative value representative ofa desired total average specific energy to be absorbed by said stock;

D. obtaining a functional relationship between static drainage rate and total absorbed refining energy that is relevant to said stock;

E. deriving a fourth quantitative value from said second value and said functional relationship that is representative of the total average specific energy that has been absorbed by said stock;

F. deriving a fifth quantitative value from the mathematical combination of said first, third and fourth values that is representative of a change in said first value for the total average specific energy absorbed by said stock, as discharged by said refining engine means, to substantially equal said third value; and,

G. controlling said refining engine means in response to said fifth value.

8. A method of controlling pulp refining engines means as described by claim 7 wherein said fifth value is proportional to the difference between said third value and the sum ofsaid first and fourth values.

9. A method of controlling pulp refining engine means as described by claim 7 additionally comprising the steps of:

A. producing signals proportional to said first, second and third values;

B. processing said second value signal pursuant to said functional relationship to produce a fourth value signal;

C. combining said first, third and fourth value signals to produce a fifth value signal; and,

D. controlling said refining engine means responsively to said fifth value signal.

10. A method of controlling pulp refining engine means as described by claim 9 wherein said second value signal is proportional to the measured time interim of a stock slowness test.

11. A system for controlling the magnitude of energy applied to an aqueous pulp slurry flow stream by refiner engine means, said system comprising:

A. means for quantitatively measuring the static drainage rate of said slurry at a station in said flow stream prior to said refiner engine means;

B. means for relating said drainage rate measurement to a first quantitative value of the total average specific energy absorbed by said slurry at the drainage rate measuring station;

C. means for comparing said first value to a second quantitative value representative of a desired total average specific energy to be absorbed by said slurry; and,

D. means for controlling the magnitude of energy applied to said slurry by refiner engine means responsive to a third quantitative value representative of a differential including said first and second values.

12. A system as described by claim 11 further comprising means for determining a fourth quantitative value representative of the average specific energy applied to said slurry by said refiner engine means.

13. A system as described by claim 12 wherein said third value represents a differential including the algebraic sum of said first and fourth values and said second value.

14. A system for controlling the magnitude of energy applied to an aqueous pulp slurry flow stream by refiner engine means, said system comprising:

A. means for quantitatively measuring the static drainage rate of said slurry at a point in said flow stream prior to said refiner engine means;

B. means for comparing said measured quantity to a second quantity representative of the static drainage rate desired for said slurry;

C. means for functionally relating the comparative differential including said measured quantity and said second quantity to a magnitude and direction of change in average specific energy applied to said slurry by refiner engine means; and,

D. means for controlling said refiner engine means responsive to the change determined by said functionally relating means.

15. A system as described by claim 14 further comprising means for determining a third quantity representative of the average specific energy applied to said flow stream by said refiner engine means.

16. A system as described by claim 15 wherein said comparing means compares the algebraic sum of said measured quantity and said third quantity to said second quantity.

17. In a pulp stock refiner engine control means having means for quantitatively measuring the average specific energy applied to a flow stream of pulp stock by refiner engine means, means to compare said applied energy measurement to a quantitative reference value and means to alter the energy applied by said refiner engine means responsive to said comparison, the improvement comprising:

A. means to quantitatively measure the static drainage rate of said pulp stock at a point in said flow stream prior to said refiner engine means; and,

B. means to relate said drainage rate value to said reference value.

18. Control means as described by claim 17 wherein said reference value represents a desired total average specific energy applied to said flow stream and said relating means determines the average total specific energy actually absorbed by said flow stream from said measured drainage rate value.

19. Control means as described by claim 18 wherein said comparison means derives the algebraic sum of said refiner engine applied energy measurement and said actually absorbed energy value and obtains the differentialbetween said sum and said reference value. 

2. A method as described by claim 1 wherein the value of total refining energy actually absorbed by said stock is derived from a known functional relationship that a static drainage rate value bears to total absorbed refining energy for a stock sample that is representative of the subject stock.
 3. A method as described in claim 2 wherein said value of total refining energy actually absorbed is derived from a measured value of static drainage rate for said subject stock.
 4. A method of controlling the magnitude of energy applied to a flow stream of aqueous slurry pulp stock by pulp refining engine means, said method comprising the steps of: A. obtaining a functional relationship between static drainage rate and total absorbed refining energy that is relevant to said stock; B. measuring the static drainage rate of said stock at a point in said flow stream before said engine means; C. deriving a first quantitative value from said measured drainage rate and said functional relationship that is representative of the total average specific energy that has been absorbed by said stock; D. selecting a second quantitative value that is representative of a desired total average specific energy to be absorbed by said stock; E. deriving a third quantitative value from the mathematical combination of said first and second values that is representative of a change in the magnitude of average specific energy delivered to said stock by said engine means necessary for said first value to substantially equal said second value; and F. controlling said engine means in response to said third value.
 5. A method of controlling pulp refining engine means as described by claim 4 additionally comprising the steps of: A. producing signals proportional to said first and second values; B. combining said first and second value signals to produce a third value signal; and C. controlling said refining engine means responsively to said third value signal.
 6. A method of controlling pulp refining engine means as described by claim 5 wherein said first value signal is proportional to the measured time interim of a stock slowness test.
 7. A method of controlling at least one pulp refining engine means comprising the steps of: A. obtaining from measured parameters a first quantitative value representative of the average specific energy applied to a pulp stock flow stream by said engine means; B. obtaining from measured parameters a second quantitative value representative of the average static drainage rate of said flow stream stock prior to working by said engine means; C. selecting a third quantitative value representative of a desired total average specific energy to be absorbed by said stock; D. obtaining a functional relationship between static drainage rate and total absorbed refining energy that is relevant to said stock; E. deriving a fourth quantitative value from said second value and said functional relationship that is representative of the total average specific energy that has been absorbed by said stock; F. deriving a fifth quantitative value from the mathematical combination of said first, third and fourth values that is representative of a change in said first value for the total average specific energy absorbed by said stock, as discharged by said refining engine means, to substantially equal said third value; and, G. controlling said refining engine means in response to said fifth value.
 8. A method of controlling pulp refining engines means as described by claim 7 wherein said fifth value is proportional to the difference between said third value and the sum of said first and fourth values.
 9. A method of controlling pulp refining engine means as described by claim 7 additionally comprising the steps of: A. producing signals proportional to said first, second and third values; B. processing said second value signal pursuant to said functiOnal relationship to produce a fourth value signal; C. combining said first, third and fourth value signals to produce a fifth value signal; and, D. controlling said refining engine means responsively to said fifth value signal.
 10. A method of controlling pulp refining engine means as described by claim 9 wherein said second value signal is proportional to the measured time interim of a stock slowness test.
 11. A system for controlling the magnitude of energy applied to an aqueous pulp slurry flow stream by refiner engine means, said system comprising: A. means for quantitatively measuring the static drainage rate of said slurry at a station in said flow stream prior to said refiner engine means; B. means for relating said drainage rate measurement to a first quantitative value of the total average specific energy absorbed by said slurry at the drainage rate measuring station; C. means for comparing said first value to a second quantitative value representative of a desired total average specific energy to be absorbed by said slurry; and, D. means for controlling the magnitude of energy applied to said slurry by refiner engine means responsive to a third quantitative value representative of a differential including said first and second values.
 12. A system as described by claim 11 further comprising means for determining a fourth quantitative value representative of the average specific energy applied to said slurry by said refiner engine means.
 13. A system as described by claim 12 wherein said third value represents a differential including the algebraic sum of said first and fourth values and said second value.
 14. A system for controlling the magnitude of energy applied to an aqueous pulp slurry flow stream by refiner engine means, said system comprising: A. means for quantitatively measuring the static drainage rate of said slurry at a point in said flow stream prior to said refiner engine means; B. means for comparing said measured quantity to a second quantity representative of the static drainage rate desired for said slurry; C. means for functionally relating the comparative differential including said measured quantity and said second quantity to a magnitude and direction of change in average specific energy applied to said slurry by refiner engine means; and, D. means for controlling said refiner engine means responsive to the change determined by said functionally relating means.
 15. A system as described by claim 14 further comprising means for determining a third quantity representative of the average specific energy applied to said flow stream by said refiner engine means.
 16. A system as described by claim 15 wherein said comparing means compares the algebraic sum of said measured quantity and said third quantity to said second quantity.
 17. In a pulp stock refiner engine control means having means for quantitatively measuring the average specific energy applied to a flow stream of pulp stock by refiner engine means, means to compare said applied energy measurement to a quantitative reference value and means to alter the energy applied by said refiner engine means responsive to said comparison, the improvement comprising: A. means to quantitatively measure the static drainage rate of said pulp stock at a point in said flow stream prior to said refiner engine means; and, B. means to relate said drainage rate value to said reference value.
 18. Control means as described by claim 17 wherein said reference value represents a desired total average specific energy applied to said flow stream and said relating means determines the average total specific energy actually absorbed by said flow stream from said measured drainage rate value.
 19. Control means as described by claim 18 wherein said comparison means derives the algebraic sum of said refiner engine applied energy measurement and said actually absorbed energy value and obtains the differential betweeN said sum and said reference value. 